Careless soldiers fail to hit target (6)
I believe the answer is:
remiss
'careless' is the definition.
(I know that careless can be written as remiss)
'soldiers fail to hit target' is the wordplay.
I cannot quite understand how this works, but
'soldiers' could be 're' (Royal Engineers) and 're' is found within the answer.
'fail' could be 'miss' (missing is a kind of failing) and 'miss' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for remiss that I've seen before include "Careless and inattentive" , "Negligent in performing duties" , "Negligent, lax" , "Failing in what duty requires" , "delinquent" .)